Low Strontium Research Articles

Synthesis and Characterization of Perovskite-Type Oxides La1−xMxCoO3 (M = Ce, Sr) for the Selective CO Oxidation (SELOX)

Perovskite-type oxides La1−xMxCoO3 (M = Ce, Sr) were prepared by citrate method, characterized and evaluated in the selective CO oxidation (SELOX-CO). The insertion of low Cerium or Strontium content generated solids with a single phase related LaCoO3 perovskite. For higher contents we observed segregation of CeO2 and SrCO3. The iso-structural substitution favors the formation of vacancies. The SELOX-CO showed 100 % CO conversion at 200 °C. Higher temperatures favored hydrogen oxidation and methanation.

A Multi‐Method Database of the Black and White Marbles of Göktepe (Aphrodisias), Including Isotopic, EPR, Trace and Petrographic Data

A database of the ancient marbles of Göktepe near Aphrodisias is reported, and includes 160 white, black and bichrome samples from 13 quarries and two waste deposits. The quarries are grouped into four districts. Districts 1 and 2, to the north, produced exclusively black or dark grey marbles (nero antico). Districts 3 and 4 produced white statuary marble. Nero antico and a black and white stone were also quarried in district 4, where the black marble surfaces again. The samples were characterized using petrography, isotopic analysis, EPR spectroscopy and trace analysis. The Göktepe white exhibits an unparalleled combination of fine grain, low EPR intensity and high strontium concentration that often allows easy identification. The isotopic values are less distinctive and similar to those for Carrara. In most cases, however, they are tightly grouped and also quite indicative. The black marbles exhibit a much weaker metamorphic overprint. With respect to the white marbles, they show analytical similarities but also notable differences. Therefore, establishing their provenance can be more difficult and may require the support of petrographic analysis. The results suggest that the Göktepe marbles were among the most prized and widespread statuary marbles used in Roman times, particularly from the early second century ad onwards.

Origin of Lower Ordovician dolomites in eastern Laurentia: Controls on porosity and implications from geochemistry

The Catoche Formation of the St. George Group in eastern Laurentia (western Newfoundland) consists of early Ordovician (Arenigian) shallow marine platform carbonates (∼160 m thick), which were extensively dolomitized during the course of their diagenetic history. The dolomites occur as both replacement and pore-filling cements and are a major control on porosity distribution in the formation. The origin and diagenetic history of the Catoche dolomites at Daniel's Harbour (western Newfoundland) were analysed in comparison to equivalent successions at Port au Choix (PaC) and Port au Port Peninsula (PaP) to assay the reservoir potential of these dolomites in eastern Laurentia. Petrographic examination identified at least three generations of dolomites in the Catoche Formation, which are: (1) an early replacement sub- to eu-hedral micritic dolomite (<4 μm–30 μm, D1), (2) eu- to sub-hedral dolomite (70 μm–1 mm) often with cloudy cores and clear rims (D2), and (3) subhedral to anhedral saddle dolomite cement (200 μm–3 mm, D3). The micritic dolomite (D1) exhibits a dull cathodoluminescence (CL) under cathodoluminoscope, whereas dolomite D2 exhibits consistent concentric CL zonation. Some subhedral crystals of D3 appear zoned both in plane polarized light and cathodoluminoscope, otherwise D3 exhibits a dull CL. Stoichiometric dolomite occurs in all three generations with D2 as the dominant dolomite by abundance.The low strontium (47 ± 25 ppm) content coupled with depleted δ18O value of dolomitizing fluids (−10 to −11.2‰ VSMOW) and near-micritic grain size, suggests an early precipitation of dolomite D1 at low temperatures of near-surface conditions from solutions likely formed by mixing of early Ordovician sea and meteoric waters. In contrast, microthermometric measurements of primary two-phase fluid inclusions in dolomite D2 (homogenization temperatures of 102–168 °C with a salinity range of 19.8–25 eq wt% NaCl) and dolomite D3 (homogenization temperatures of 158–190 °C with a salinity range of 20.2–22.2 eq wt% NaCl), suggest that both dolomite generations were generated in mid to deep burial settings from high salinity, low temperature (<200 °C) hydrothermal fluids likely under suboxic conditions. This is consistent with the low Sr concentrations for D2 (36.4 ± 8 ppm) and D3 (38.7 ± 9 ppm), δ18O values of dolomitizing fluids for D2 (+2.1 to +8.1‰, VSMOW) and D3 (+6 to +8.1‰ VSMOW), coupled with Fe contents of D2 (1684 ± 1096 ppm) and D3 (1783.7 ± 618 ppm) as well as the respective Mn (D2 = 131.2 ± 50 and D3 = 197.5 ± 55 ppm) concentrations.ΣREE and shale normalized (REESN) values of Catoche carbonates indicate enrichment in rare earth element (REE) composition of the earliest calcite (C1) relative to those of Arenig seawater, whereas the REESN profiles of the dolomite generations mimic that of calcite C1. The Ce (Ce/Ce*)SN and La (La/La* = Pr/Pr*)SN anomalies of the Catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas Eu (Eu/Eu*)CN anomalies suggest similar source fluids for D2 and D3. Results of fluid inclusion gas analysis are consistent with petrographic features and geochemical compositions and support the exclusion of magmatic fluids during dolomitization. Visual estimates of porosity (ϕ) from thin sections indicate four porous (ϕ = 4–12) horizons. Vugs and intercrystalline pores are two types of porosity associated with the dolomites with the latter being the dominant type and associated mainly with dolomite D2.

In-situ scanning photoelectron microscopy study of operating (La,Sr)FeO3-based NOx-sensing surfaces

Scanning photoelectron microscopy and impedance spectroscopy were used to study simultaneously the impact of NO gas on surface chemistry and the electrochemical response of electrolyte-supported (La1−xSrx)FeO3−δ (LSF) sensing layers in electrochemical NOx sensors, during high-temperature operation. Electrochemical model cells were fabricated by screen printing macro- and micro-patterned thin films on zirconia electrolyte. Cell bias, temperature and NO/O2 gas ratio were varied during the experiments.LSF/3YSZ sensing layers remained stable over a wide temperature-bias range in an oxygen-containing environment. LSF compositions with low strontium content (x=0.2) did not undergo any changes in their surface chemistry, while compositions with higher strontium level (x=0.4) showed partial reduction of surface iron at low oxygen chemical potential. Upon exposure to NO gas at low oxygen partial pressure, NO was observed to dissociate on the LSF surface and form chemisorbed O- and N-adatoms with strong interactions to surface iron or zirconium. Concentration and stability of these ad-complexes increased with the NO/O2 ratio, cathodic bias and decreasing temperature. At low NO level in the gas, NO was observed to interact preferentially with iron atoms at the LSF surface and the surface reaction was reversible. At high NO/O2 ratios and low temperatures, irreversible formation of surface ad-complexes was observed, with reduced iron and zirconium, and caused even new phase formation.Simultaneous assessment of surface chemistry and cell impedance demonstrated that modifications in surface chemistry directly affected the oxygen exchange rate in the cell. In the presence of NO, the sensing oxide resistance decreased for zero or small bias. For large bias, no additional decrease in cell resistance was observed beyond the corresponding intrinsic cell performance in oxygen. Under these conditions, again, the particular cell response depended on the strontium substitution level in LSF, favoring lower redox-stability and thus a more complicated cell response to NO gas for high strontium level.

The new data on the origin of the Patom Crater (East Siberia)

It has been found that the origin of the Patom Crater is related to endogenous processes with the main role played by deep flow of fluid components, which determine formation of the ejecta cone at about 500 years ago or more. This is evidenced by the zonal structure of the crater and geochemical peculiarities of rocks, caused by the long formation time for particular zones. Sandstone and schist blocks that were included into eruptive breccia within the crater were affected by gaseous or fluid components and intensively carbonized. During carbonatization, these rocks within the crater were being enriched in Ca and Sr, but the shares of the 87Sr and, consequently, 87Sr/86Sr ratio in them abruptly decrease. This is explained by the influence of deep fluids on terrigenous rocks, which were initially depleted in the radiogenic strontium isotope and might flow from a magmatic source with a low 87Sr/86Sr ratio. However, these fluids were enriched in CO2 and transported significant quantities of Sr, which led to enrichment of all terrigenous rocks in the crater in this element. The discovery of individual sandstone blocks with high concentrations of summarized rare earth elements (up to 557 g/t) and higher Sr and Ba contents among the fragments of host stratum within the Patom Crater allows us to suppose that there is a magmatic source enriched in fluid components at depths. The effect of the active fluid phase with low strontium isotopic ratios on rocks during the Patom Crater formation might lead to an abrupt decrease in values of the initial 87Sr/86Sr ratio in carbonized sandstones and schists.

The intact strontium ranelate complex stimulates osteoblastogenesis and suppresses osteoclastogenesis by antagonizing NF-κB activation

Strontium ranelate, a pharmaceutical agent shown in clinical trials to be effective in managing osteoporosis and reducing fracture risk in postmenopausal women, is relatively unique in its ability to both blunt bone resorption and stimulate bone formation. However, its mechanisms of action are largely unknown. As the nuclear factor-kappa B (NF-κB) activation antagonists both stimulate osteoblastic bone formation and repress osteoclastic bone resorption, we hypothesized that strontium ranelate may achieve its anabolic and anti-catabolic activities by modulating NF-κB activation in bone cells. In this study, osteoclast and osteoblast precursors were treated with intact strontium ranelate or its individual components sodium ranelate and/or strontium chloride, and its effect on in vitro osteoclastogenesis and osteoblastogenesis and on NF-κB activation quantified. Although the activity of strontium ranelate has been attributed to the release of strontium ions, low dose intact strontium ranelate complex, but not sodium ranelate and/or strontium chloride, potently antagonized NF-κB activation in osteoclasts and osteoblasts in vitro, and promoted osteoblast differentiation while suppressing osteoclast formation. Taken together, our data suggest a novel centralized mechanism by which strontium ranelate promotes osteoblast activity and suppresses osteoclastogenesis, based on suppression of NF-κB signal transduction. We further demonstrate that the biological actions of strontium ranelate may be related to low dose of the intact molecule rather than dissociation and release of strontium ions, as previously thought. These data may facilitate the development of additional novel pharmacological agents for the amelioration of osteoporosis, based on NF-κB blockade.

Preparation and characterization of nanocrystalline and mesoporous strontium titanate thin films at room temperature

The low temperature perovskite-type strontium titanate (SrTiO3) thin films and powders with nanocrystalline and mesoporous structure were prepared by a straightforward particulate sol–gel route. The prepared sol had a narrow particle size distribution with hydrodynamic diameter of about 17 nm. X-ray diffraction (XRD) revealed that the synthesized powders had a perovskite-SrTiO3 structure with preferable orientation growth along the (1 0 0) direction. TEM images showed that the average crystallite size of the powders annealed in the range 300–800°C was around 8 nm. FE-SEM analysis and AFM images revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 25 nm at 600°C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure with BET surface area in the range 92–75 m2/g at 400–600°C. One of the smallest crystallite sizes and one of the highest surface areas reported in the literature were obtained, which can be used in many applications, such as photocatalysts.

Improved properties of Ti6Al4V by means of nitrogen high temperature plasma based ion implantation

A stable heating source, providing steady temperatures in the range of 200 to more than 1000°C, was used to perform high temperature plasma based ion implantation (PBII) on Ti6Al4V. The precise control of the heating of the samples in vacuum while performing PBII is accomplished by means of an efficient electron source, working independent of the conditions of the discharge.The electrons produced by a low work function (2.1eV) barium, strontium and calcium oxide cathode help with the start-up of the discharge, with the increase of nitrogen ionization and heating of the samples. The large growth of the treated layer thickness was a result of the thermal diffusion of nitrogen, reaching up to 20μm, in the total process time lasting only 100min. Experiments were run by setting a constant substrate temperature during PBII to 800°C but varying the pulse intensity and the duration of the process. Our results showed improvements of the mechanical and tribological properties, and also higher resistance to corrosion of the samples treated by high temperature PBII.

Effect of Strontium Addition on the Microstructures and Mechanical Properties of Mg-5Al-3Ca Alloys

The effect of adding up to 4 mass% of strontium to Mg-5Al-3Ca alloys was investigated in terms of microstructural and mechanical properties. The major interdendritic intermetallic compounds of as-cast alloys changed from the Mg2Ca phase to a combination of the (Mg,Al)2Ca and Al4Sr phases. The morphology of the interdendritic � -Mg/Al4Sr eutectic phase also changed from a coarse lamellar structure at a low strontium concentration to a bulk-like ultrafine lamellar structure at a high strontium concentration (4 mass%). The creep resistance was improved by the addition of up to 2 mass% strontium but it was saturated at a higher strontium concentration. [doi:10.2320/matertrans.M2010387]

Fingerprinting a multistage metamorphic fluid–rock history: Evidence from grain scale Sr, O and C isotopic and trace element variations in high-grade marbles from East Antarctica

Granulite grade marble layers interlayered with metapelitic granulites from Lützow Holm Bay, East Antarctica, provide insight into fluid–rock interactions during burial to and exhumation from lower crustal levels. Sub-millimeter scale strontium, oxygen and carbon isotope variations along with LA-ICPMS trace element geochemistry and mineral chemistry of texturally characterized carbonates and associated minerals helped to reconstruct the multistage metamorphic fluid history. Fluid–rock interaction dating back to prograde metamorphism are still preserved in consistently low oxygen and high strontium isotope compositions ( δ 18O = 12‰; 87Sr/ 86Sr (550Ma) = 0.7248) within a massif dolomitic marble layer that escaped significant later metasomatism. In most marbles, total re-crystallization and isotopic resetting occurred in the presence of “externally derived” hyper-saline fluids that circulated along the carbonate layers during the early stages of prograde metamorphism. This leads to a trend of increased radiogenic Sr in marbles towards the value of associated metapelitic rocks that have 87Sr/ 86Sr (550Ma) of 0.764. LA-ICPMS studies on trace elements in carbonate and associated silicate minerals at different textural settings, distinguished using cathodoluminescence microscopy, revealed multiple metasomatic events during retrograde metamorphism. Trace element contents of Ba, Sr, Pb and U gave compelling evidence for metasomatic alteration that postdate the exsolution of carbonate at ~ 600 ºC, which can be correlated with the fluids released from the crystallization of anatectic melts and pegmatites. Subsequently, meteoric fluid infiltration occurred at a shallower level of the crust and caused extreme oxygen isotopic heterogeneity ( δ 18O = 14.7 ~ − 4.9‰) and imprinted high concentration of fluid mobile elements. Taken together our results emphasize the importance of integrating textural and chemical heterogeneities to reveal the multiple episodes of fluid–rock interaction processes in a dynamic continental crust, which has major implications on migration of fluids and material and help in formulating models on the geodynamic evolution of crust.

Asynchronous Transmitter Release from Cholecystokinin-Containing Inhibitory Interneurons Is Widespread and Target-Cell Independent

Neurotransmitter release at most central synapses is synchronized to the timing of presynaptic action potentials. Here, we show that three classes of depolarization-induced suppression of inhibition-expressing, cholecystokinin (CCK)-containing, hippocampal interneurons show highly asynchronous release in response to trains of action potentials. This asynchrony is correlated to the class of presynaptic interneuron but is unrelated to their postsynaptic cell target. Asynchronous and synchronous release from CCK-containing interneurons show a slightly different calcium dependence, such that the proportion of asynchronous release increases with external calcium concentration, possibly suggesting that the modes of release are mediated by different calcium sensors. Asynchronous IPSCs include very large (up to 500 pA/7nS) amplitude events, which persist in low extracellular calcium and strontium, showing that they result from quantal transmitter release at single release sites. Finally, we show that asynchronous release is prominent in response to trains of presynaptic spikes that mimic natural activity of CCK-containing interneurons. That asynchronous release from CCK-containing interneurons is a widespread phenomenon indicates a fundamental role for these cells within the hippocampal network that is distinct from the phasic inhibition provided by parvalbumin-containing interneurons.

In vitrodevelopment of goat parthenogenetic and somatic cell nuclear transfer embryos derived from different activation protocols

Oocyte activation is an essential step in animal cloning to allow subsequent development of the reconstructed embryos. A special activation protocol is required for different animal species. The present study investigated low temperature, electrical pulses, ethanol, ionomycin and strontium for goat oocyte activation in order to optimize the protocols. We found, as a result, effective activation and parthenogenetic development of goat oocytes that had been derived from ionomycin, strontium and electrical pulse groups. Within each group 79.3-81.6%, 2.2-78.8% and 65.5% of the oocytes cleaved and 16.2-24.8%, 0-15.6% and 11.1% of the cleaved embryos developed into blastocysts when the oocytes were activated by ionomycin combined with 6-dimethylaminopurine, strontium plus cytochalasin B and electrical pulses combined with cytochalasin B, respectively. However, low temperature and ethanol were both unable to activate goat oocytes under our experimental conditions. When ionomycin combined with 6-dimethylaminopurine and strontium plus cytochalasin B was applied to activate somatic cell nuclear transfer embryos derived from cultured cumulus, 51.0% and 72.5% of the embryos cleaved, respectively. After transfer of 4-cell embryos into recipients, one (1/19 and 1/7) of the recipients from each group was found to be pregnant as detected by ultrasound, but both of these recipients lost the embryos between 45 and 60 days of pregnancy.

PROVENANCE OF ANCIENT TEXTILES—A PILOT STUDY EVALUATING THE STRONTIUM ISOTOPE SYSTEM IN WOOL*

Strontium isotopes are used in archaeology to reconstruct human and animal migration routes. We present results of a pilot study applying strontium isotope analyses to modern sheep hair as a basis for its potential use as a provenance tracer for ancient woollen textiles. Our hydrofluoric acid‐based, lipid soluble analytical protocol, also tested on a number of ancient textile fibres, allows for contamination‐free, low blank strontium isotope analysis of minimal amounts of archaeological material. 87Sr/86Sr ratios of decontaminated sheep hair agree well with the compositions of biologically available (soluble) strontium fractions from the respective feeding ground soils, a translatable requirement for any potentially successful provenance tracing applied to wool textiles.

Evidence for biocycling from Ba/Ca, Sr/Ca, and 87Sr/86Sr in soils (Red Brown Earths) from South Australia

The impact of elemental cycling and biological fractionation in the soil–vegetation system was investigated for 6 Red Brown Earth soil profiles (Xeralfs and Xerults) from South Australia by comparing geochemical and 87Sr/86Sr data from bulk soils, soil exchange pool, and vegetation (grapes). In all 6 soil profiles from 3 different sites, Ba/Ca ratios of vegetation, soil exchange pool, and bulk soils were found to be a more robust biological fractionation indicator than Sr/Ca ratios. In the base-poor soils of the Coonawarra–Padthaway area of South Australia, the degree of weathering of soil material, as estimated by titania and alumina contents, correlated very well with the biological fractionation indicator Ba/Ca. Soil horizons with greater clay and titania content also had higher degrees of biological fractionation. Similar Red Brown Earth soils 400 km north in the Clare Valley showed either no, or poor, biological fractionation signature in their bulk soil. The Clare Valley soils have a stronger colluvial component and are richer in base cations than the Coonawarra and Padthaway sites. The main source of bulk soil material in the base-poor soils of the Coonawarra–Padthaway areas is dust, which has greatly influenced the base cation concentration, Ba/Ca ratios, and the strontium isotope ratios. Soils from Clare Valley, by comparison, are less intensely weathered and are thus not as dependent on dust and biocycling for their base cations. Biological fractionation has not left a discernible signature on the composition of the bulk soil. The exchange pools at all 3 sites are dominated by wetfall–dryfall sources, which in this coastal area are dominated by marine sources. For the base-poor soils of the Coonawarra–Padthaway area, the most likely major source of aeolian detritus is Murray River mud. The fine-grained component of this mud, with its organic matter content, relatively high base cation concentrations, and low strontium isotope ratios (Douglas et al. 1995) appears to have overwhelmed other dust sources and caused a homogenisation of the geochemical signature of fine-grained bulk soils in this area. Subsequent in situ weathering and neoformation following dust deposition were strongly influenced by exchange phase concentrations and ratios and resulted in an enhanced biological fractionation signature of the soils.

A New Thermionic Cathode Based on Carbon Nanotubes with a Thin Layer of Low Work Function Barium Strontium Oxide Surface Coating

ABSTRACTWe have created a thermionic cathode structure that consists of a thin tungsten ribbon; carbon nanotubes (CNTs) on the ribbon surface; and a thin layer of low work function barium strontium oxide coating on the CNTs. This oxide coated CNT cathode was designed to combine the benefits from the high field enhancement factor from CNTs and the low work function from the emissive oxide coating. The field emission and thermionic emission properties of the cathode have been characterized. A field enhancement factor of 266 and a work function of 1.9 eV were obtained. At 1221 K, a thermionic emission current density of 1.22A/cm2 in an electric field of 1.1 V/μm was obtained, which is four orders of magnitude greater than the emission current density from the uncoated CNT cathode at the same temperature. The high emission current density at such a modest temperature is among the best ever reported for an oxide cathode.

Estimating groundwater mixing and origin in an overexploited aquifer in Guanajuato, Mexico, using stable isotopes (strontium-87, carbon-13, deuterium and oxygen-18)†

Stable Isotopes (strontium-87, deuterium and oxygen-18, carbon-13) have been used to reveal different sources of groundwater and mixing processes in the aquifer of the Silao-Romita Valley in the state of Guanajuato, Mexico. Calcite dissolution appeared to be the main process of strontium release leading to relatively equal 87Sr/86Sr ratios of 0.7042–0.7062 throughout the study area which could be confirmed by samples of carbonate rocks having similar Sr ratios (0.7041–0.7073). δ13C values (−11.91– −6.87‰ VPDB) of groundwaters confirmed the solution of carbonates but indicated furthermore influences of soil-CO2. Deuterium and 18O contents showed a relatively narrow range of−80.1– −70.0 ‰ VSMOW and−10.2– −8.8 ‰, VSMOW, respectively but are affected by evaporation and mixing processes. The use of δ13C together with 87Sr/86Sr revealed three possible sources: (i) carbonate–controlled waters showing generally higher Sr-concentrations, (ii) fissure waters with low–strontium contents and (iii) infiltrating water which is characterized by low δ13C and 87Sr/86Sr ratios. The third component is affected by evaporation processes taking place before and during infiltration which might be increased by extraction and reinfiltration (irrigation return flow).

Effect of sintering optimization on the electrical properties of bulk Ba xSr 1−xTiO 3 ceramics

Ba x Sr 1− x TiO 3 ( x=0.6, 0.75, 0.80, 0.85 and 0.9) compositions are prepared by solid-state reaction route using controlled heating and cooling. Density optimization by varying sintering temperature was achieved. X-ray diffraction (XRD) analysis shows the phase pure materials. The lattice constant decreases from 3.9868 Å ( x=0.90) to 3.9449 Å ( x=0.60) with increasing Sr 2+; the tetragonal distortion also decreases. Dielectric constant show sharp peaks for samples having low strontium content (0.10, 0.15) and gets smeared out as the strontium content is increased (0.20, 0.25). For further higher Sr 2+ composition (0.40), the dielectric peak could not be observed in the measured temperature range. The peak broadening in Sr 2+ rich compositions indicates that diffused transitions and is attributed to the disorder in the arrangement of cations at A-site. A modified Curie–Weiss law using exponent γ and diffuseness parameter δ fits temperature dependence of dielectric constant in paraelectric phase. Both the parameters increase with increasing Sr 2+ content showing that with strontium substitution, the material becomes disordered and may be correlated with the compositional fluctuation in solid solution. Frequency dependence of dielectric behavior is analyzed in terms of Debye formalism and nature of dielectric relaxation processes is explored using Cole–Cole formalism. Ferroelectric hysterisis loops reveal spontaneous polarization and coercive field increases with deceasing Sr content.

Misidentification of the migratory history of anguillid eels by Sr/Ca ratios of vaterite otoliths

Most fish otoliths are composed of aragonite, but occasionally they form a mosaic with its polymorph, vaterite. We found an unusual mosaic structure of extremely low strontium to calcium (Sr/Ca) ratio in the aragonite otoliths of European eels Anguilla anguilla. The mosaic crystal structure in the eel otolith appeared opaque under reflected light after EDTA etching and was confirmed to be a vaterite crystal by Raman spectroscopy. Analysis by laser ablation inductively coupled plasma mass spectrometry indicated that the elements sodium (Na), strontium (Sr) and barium (Ba) were lower in abundance and magnesium (Mg) and manganese (Mn) were higher in the vaterite than in the aragonite. Otoliths with vaterite inclusions were found in 48.1% of the 108 eels examined. If the mosaic vaterite in otoliths is not identified and avoided, the migratory environmental history of fish could be misidentified when otolith elemental signatures are used as biological tracers.

Enhanced field emission from carbon nanotubes with a thin layer of low work function barium strontium oxide surface coating

The authors report a field emitter structure based on barium strontium oxide coated carbon nanotubes (CNTs). This emitter consists of a thin tungsten ribbon with CNTs on the surface, and a thin layer of low work function barium strontium oxide coating on the CNTs. CNTs were grown on the surface of the tungsten ribbon by plasma enhanced chemical vapor deposition, and the oxide coatings were prepared using magnetron sputtering. This oxide coated CNT emitter was designed to combine the benefits of the high field enhancement factor from CNTs and the low work function from the emissive oxide coating. The field emission properties of the emitters were characterized. A field enhancement factor of 478 and a work function of 1.9eV were obtained for the oxide coated CNTs. As a result of the reduction of surface work function, the field emission from the oxide coated CNTs increased by a factor of 2–3 compared to the uncoated CNTs. At 4.4V∕μm, the field emission current of 23.6μA was obtained from an emitting surface of 0.012cm2.

Sr2+ doping effects on the transport and magnetic properties of GdBaCo2O5+δ

Studies on some new members of the cobalt perovskite Gd1−xSrxBaCo2O5+δ with low strontium concentrations (0<x<0.1) have been carried out with the aim of investigating possible metallization of the GdBaCo2O5+δ system by hole doping. Low temperature electrical resistivity, magnetic susceptibility and thermopower of the above system have been studied. The pristine compound with x=0 and δ∼0.5 exhibits a semiconductor-like behavior and two magnetic transitions below room temperature. Upon Sr2+ substitution, there is a fall in resistivity by 2–3 orders of magnitude at low temperature and also a dramatic reduction in the ferromagnetic to antiferromagnetic transition temperature. These changes can be explained on the basis of hole doping (and increase in the Co4+content). Evidence for an increase in Co4+ with Sr2+ substitution is provided by iodometric analysis.